JMHO, but the brake fluid should be changed ever so often and at 5 years of age, it's due. Brake fluid attracts moisture which in turn starts the corrosion process on master cylinders, calipers, wheel cylinders, etc. Aluminum does not rust but it will pit and once pitted it is recommended that the part be replaced rather than attempt a rebuild.
Now to address the question of why the maintenance schedule does not mention this. It's simple. Car makers, and not just Toyota, promote the idea that their vehicles are close to maintenance free. Skip this, skip that, put this or that off until xxxx freezes over, etc. They don't want the car owners to even consider for one minute the amount of money spent on preventative maintenance.
There's a lot of other things that are not recommended that should be done no matter what the maintenance schedules state.
Transmission fluid should be changed at 30k miles intervals, fuel filters at 15-20k mile intervals, spark plugs should never be left in for 100k miles, etc, etc.
Some car makers even state that mechanical valve lifters should not be inspected/adjusted until well over a 100k miles or even never. This of course is also wrong headed. If the car makers feel so strongly about this issue then they should provide a lifetime warranty for that certain number of people who are going to suffer engine damage because they DID follow the recommendations to ignore it until whenever.